Core material for composite structures

ABSTRACT

A unitary core panel for a composite sandwich structure includes a plurality of cell walls defining a plurality of core cells, the plurality of cell walls extending across a thickness of the core, the plurality of core cells including one or more defined structural nonuniformities resulting in nonuniform properties of the core panel. A method of forming a core panel for a composite sandwich structure includes determining structural requirements of the core panel, designing the core panel to satisfy the structural requirements with one or more local nonuniformities in the core panel, and manufacturing the core panel as a unitary core panel with the one or more local nonuniformities.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application of PCT/US2016/038654,filed Jun. 22, 2016, which claims the benefit of U.S. ProvisionalApplication No. 62/182,954, filed Jun. 22, 2015, both of which areincorporated by reference in their entirety herein.

BACKGROUND

The subject matter disclosed herein generally relates to compositestructures. More specifically, the present disclosure relates to corematerials for composite structures.

Light weight composite structures often comprise a sandwich structurewith a honeycomb core positioned between and adhered to a skin at eitherside of the honeycomb core. In the current state of the art the core isformed as a bulk product as a panel with a plurality of hexagonal cellsof fixed and uniform size and orientation, defining the properties ofthe core panel. The core panel is typically formed from a plurality ofribbons of material, formed into the hexagonal cells and adhered to eachother. Due to the manufacturing process, the core panel has inherentlydifferent orthogonal properties in different directions, based on aribbon direction of the core panel. Because of the directional nature ofthe core material properties, the material selection for a givenstructure is often constrained by the lowest properties of the corematerial and the highest stress condition identified for the structure.This leads to substantial constraints in structural design andoptimization, and structures are as a result, heavier than necessary.

BRIEF SUMMARY

In one embodiment, a unitary core panel for a composite sandwichstructure includes a plurality of cell walls defining a plurality ofcore cells, the plurality of cell walls extending across a thickness ofthe core, the plurality of core cells including one or more definedstructural nonuniformities resulting in nonuniform properties of thecore panel.

Additionally or alternatively, in this or other embodiments thestructural nonuniformity is one or more of nonuniform core cell density,nonuniform core cell shape, or nonuniform core cell size.

Additionally or alternatively, in this or other embodiments the corecell density is increased in areas of the core panel with increasedstresses.

Additionally or alternatively, in this or other embodiments the corecell size is decreased in areas of the core panel with increasedstresses.

Additionally or alternatively, in this or other embodiments thenonuniformity includes a variation in cell wall thickness.

Additionally or alternatively, in this or other embodiments the corepanel is formed via one of material deposition.

Additionally or alternatively, in this or other embodiments one or morematerial properties of the core panel material vary across the corepanel or through a core panel thickness.

Additionally or alternatively, in this or other embodiments one or moreend flanges are located at a cell wall.

In another embodiment, a composite sandwich structure includes a skinand a core panel adhered to the skin. The core panel includes aplurality of cell walls defining a plurality of core cells, theplurality of cell walls extending across a thickness of the core, theplurality of core cells including one or more defined structuralnonuniformities resulting in nonuniform properties of the core panel.

Additionally or alternatively, in this or other embodiments thestructural nonuniformity is one of nonuniform core cell density,nonuniform core cell shape, or nonuniform core cell size.

Additionally or alternatively, in this or other embodiments the corecell density is increased in areas of the core panel with increasedstresses.

Additionally or alternatively, in this or other embodiments the corecell size is decreased in areas of the core panel with increasedstresses.

Additionally or alternatively, in this or other embodiments thenonuniformity includes a variation in cell wall thickness.

Additionally or alternatively, in this or other embodiments the corepanel is formed via material deposition.

Additionally or alternatively, in this or other embodiments one or morematerial properties of a core panel material vary across the core panelor through a core panel thickness.

Additionally or alternatively, in this or other embodiments one or moreend flanges are located at a cell wall.

In yet another embodiment, a method of forming a core panel for acomposite sandwich structure includes determining structuralrequirements of the core panel, designing the core panel to satisfy thestructural requirements with one or more local nonuniformities in thecore panel, and manufacturing the core panel as a unitary core panelwith the one or more local nonuniformities.

Additionally or alternatively, in this or other embodiments the corepanel is manufactured utilizing an additive manufacturing process.

Additionally or alternatively, in this or other embodiments the whereinthe local nonuniformity is one or more of nonuniform core cell density,nonuniform core cell shape, or nonuniform core cell size.

Additionally or alternatively, in this or other embodiments one or morematerial properties of the core panel material vary across the corepanel or through a core panel thickness.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter is particularly pointed out and distinctly claimed atthe conclusion of the specification. The foregoing and other features,and advantages of the present disclosure are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a cross-sectional view of an embodiment of a compositesandwich structure;

FIG. 2 is a plan view of an embodiment of a core panel with varying corecell sizes and other features for a composite sandwich structure;

FIG. 3 is a plan view of another embodiment of a core panel for acomposite sandwich structure illustrating varying core cell shapes andfeatures;

FIG. 4 is a cross-sectional view of yet another embodiment of a corepanel for a composite sandwich structure, illustrating varying core cellwall thicknesses and other features;

FIG. 5 is a plan view of still another embodiment of a core panel for acomposite sandwich structure illustrating varying core cell wallthicknesses and other features;

FIG. 6 is a cross-sectional view of another embodiment of a core panelfor a composite sandwich structure, illustrating core cells with endflanges and other features;

FIG. 7 is an end view of yet another embodiment of a core panel for acomposite laminate structure illustrating a curved core cell panel andother features; and

FIG. 8 is a schematic illustration of a method of manufacturing a corepanel.

The detailed description explains embodiments of the present disclosure,together with advantages and features, by way of example with referenceto the drawings.

DETAILED DESCRIPTION

Referring to the cross-sectional view of FIG. 1, a composite sandwichpanel 10, used for example to construct skins, frames, bulkheads and/orbeam structures, includes a first skin 12 and a second skin 14 with acore panel 16 sandwiched between the first skin 12 and the second skin14, and adhered to the first skin 12 and the second skin 14. The corepanel 16 includes a plurality of cells 18, each cell 18 defined as acell opening 20 bounded by a cell wall 22. The cell wall 22 extends fromthe first skin 12 to the second skin 14. The first skin 12 and thesecond skin 14 may be formed from a variety of materials, such asfiberglass, carbon fiber material, or a metal material such as titaniumor aluminum. Further the first skin 12 and/or the second skin 14 may beformed from a single layer of material, or may alternatively be amultilayer laminate structure formed with a plurality of skin layers 24or plies adhered to each other. The first skin 12 and the second skin 14may be preformed before adhering to the core panel 16 or may be formedin the same process as the sandwich panel 10.

Referring to FIG. 2, an embodiment of a core panel 16 is shown. The corepanel 16 is formed to have engineered non-uniform properties along apanel length 26, panel width 28, and/or panel thickness 30 (shown inFIG. 1). The properties are engineered to be non-uniform in order tolocally optimize the properties of core panel 16 relative to core panel16 weight. Specifically, characteristics of the core panel 16 are variedthroughout the core panel 16 such that each portion of the core panel 16is designed based on the stresses encountered or anticipated by theportion of the core panel 16, without needing to overdesign the corepanel 16.

For example, referring to FIG. 2, in some embodiments, a density of corecells 18 is varied based on the anticipated stresses. In a relativelyhigh stress area 32, the core cells 18 are smaller sized and moretightly packed, while in a relatively low stress area 34, the core cells18 are larger.

In other embodiments, such as shown in FIG. 3, core cell 18 shape and/ororientation is modified based on the stress levels or other requirementsof the design. For example, as shown, the core panel 16 may be formedfrom core cells 18 that are triangular, rectangular, or other polygonshape. The core cells 18 may vary in size, shape and/or orientation inthe panel. In such a structure, cell walls 22 may be oriented to followan anticipated design load path through the core panel 16. The corepanel 16 may include other features such as integrated fastenerlocations 36 used for later assembly steps. The fastener locations 36may include a reinforcement zone 38 of substantially solid core panel 16material around the fastener location 36. Further, the core panel 16 mayinclude curvilinear cell walls 22.

Referring to the cross-sectional view of FIG. 4 and the plan view ofFIG. 5, in other embodiments, a cell wall thickness 40 is varied along acell height 42 and/or cell wall length 60, and may include stiffeningribs 44 or other localized features, such as slits or openings. Inaddition to, or as an alternative to varying cell wall thickness 40, thecell wall 22 material itself may be varied in the cell wall 22. Forexample, a first material may be used for a first portion of the cellwall 22, while a second material is utilized for a second portion of thecell wall 22, to locally vary selected properties of the core panel 16.Further, referring again to FIG. 3, the material may also be varied bycore panel 16 section. For example, a first core panel portion 46 (shownin FIG. 2) may be formed from a first material, while a second corepanel portion 48 (shown in FIG. 2) may be formed from a second materialhaving different selected properties than the first material. As well asproviding design flexibility to meet structural load requirements, thematerials and core panel 16 configuration may be selected to locallyvary conductivity, such as electrical or thermal conductivity, or tolocally tune vibration damping or other properties of the core panel 16.

In another embodiment, shown in FIG. 6, the core panel 16 is formed withan end flange 50 at some of the core cells 18 to increase surface areafor adhesion to the first skin 12 and/or second skin 14. Additionally,in some embodiments, the core panel 16 may be formed with a closed cellend 52 at one or more ends of the core cell 18. In other embodiments, asshown in FIG. 7, the core panel 16 is formed with one or more radius ofcurvature 54 to form a contoured sandwich panel (not shown)

It is to be appreciated that while for clarity of the description anddrawings, the core cell 18 modifications or nonuniformities arepresented separately, one skilled in the art will readily recognize thatthe nonuniformities shown in FIGS. 2-7 may be combined in design of thecore panel 16.

Core panels with engineered non-uniform properties such as in thepresent disclosure allows for core panels 16 to be engineered to haveprecisely the mechanical properties required by the design. Further,those properties can be continuously tailored to change from one area ofthe core panel to another as engineering requirements vary foroptimization of the core panel. Additionally, such core panels allow fora reduction in core splicing and potting, which require additionalmanufacturing steps such as trimming, forming, and stabilizing. A methodof manufacturing a core panel 16 is illustrated in FIG. 8. Structuraland/or dimensional requirements for a core panel 16 are determined inblock 100. The core panel 16 is designed with localized variations asdescribed above utilizing, for example, finite element analysis or otherdesign and analysis tools in block 102. This design is modified oriterated until the selected requirements are met by the core panel 16.Once the core panel design is established, the core panel 16 ismanufactured at block 104 by one or more manufacturing methods based onthe material utilized and/or the desired structure of the core panel 16.These manufacturing methods may include additive manufacturing methodssuch as material deposition, 3-D printing, laser sintering, or the like.Such manufacturing processes allow for the formation of a unitary corepanel 16 having locally varied properties and dimensional features asdescribed above. Additive manufacturing methods used in formation of thecore panel 16 provide a high degree of flexibility in fabricationoptions enabling local optimization.

Core panels with engineered non-uniform properties such as in thepresent disclosure allow for core panels to be engineered to haveprecisely the mechanical properties required by the design. Further,those properties can be continuously tailored to change from one area ofthe core panel to another as engineering requirements vary foroptimization of the core panel. Additionally, such core panels allow fora reduction in core splicing and potting, which require additionalmanufacturing steps such as trimming, forming, and stabilizing.

While the present disclosure has been described in detail in connectionwith only a limited number of embodiments, it should be readilyunderstood that the present disclosure is not limited to such disclosedembodiments. For instance, the core panel and composite sandwich paneldescribed herein may be utilized in a variety of applications, such asaircraft, wind turbines, maritime propulsion, ground transportation(bus, rail, truck, etc.) Further, the present disclosure can be modifiedto incorporate any number of variations, alterations, substitutions orequivalent arrangements not heretofore described, but which arecommensurate in spirit and/or scope. Additionally, while variousembodiments have been described, it is to be understood that aspects ofthe present disclosure may include only some of the describedembodiments. Accordingly, the present disclosure is not to be seen aslimited by the foregoing description, but is only limited by the scopeof the appended claims.

What is claimed is:
 1. A unitary core panel for a composite sandwichstructure comprising: a plurality of cell walls defining a plurality ofcore cells, the plurality of cell walls extending across a thickness ofthe core, the plurality of core cells including one or more definedstructural nonuniformities resulting in nonuniform properties of thecore panel, wherein the structural nonuniformities include at least onecell wall of the plurality of cell walls having a cell wall thickness ofa core cell varied in a direction between a first skin and a second skinin which the at least one cell wall comprises a greater cell wallthickness in a middle portion than end portions in the direction betweenthe first skin and the second skin.
 2. The core panel of claim 1,wherein the structural nonuniformity is one or more of nonuniform corecell density, nonuniform core cell shape, or nonuniform core cell size.3. The core panel of claim 2, wherein the core cell density is increasedin areas of the core panel with increased stresses.
 4. The core panel ofclaim 2, wherein the core cell size is decreased in areas of the corepanel with increased stresses.
 5. The core panel of claim 1, wherein thenonuniformity includes a variation in cell wall thickness.
 6. The corepanel of claim 1, wherein the at least one cell wall or another at leastone cell wall of the plurality of cell walls comprises a first materialand a second material different from the first material.
 7. The corepanel of claim 1, wherein one or more material properties of the corepanel material vary across the cell wall thickness.
 8. The core panel ofclaim 1, further comprising one or more end flanges disposed at a cellwall.
 9. A method of forming a core panel for a composite sandwichstructure, comprising: determining structural requirements of the corepanel; designing the core panel to satisfy the structural requirementswith one or more local nonuniformities in the core panel; andmanufacturing the core panel as a unitary core panel with the one ormore local nonuniformities, wherein the one or more localnonuniformities include at least one cell wall of the plurality of cellwalls having a cell wall thickness of a core cell varied in a directionbetween a first skin and a second skin in which the at least one cellwall comprises a greater cell wall thickness in a middle portion thanend portions in the direction between the first skin and the secondskin.
 10. The method of claim 9, wherein the core panel is manufacturedutilizing an additive manufacturing process.
 11. The method of claim 9,wherein the local nonuniformity is one or more of nonuniform core celldensity, nonuniform core cell shape, or nonuniform core cell size. 12.The method of claim 9, wherein one or more material properties of thecore panel material vary through the cell wall thickness.